1. Field of the Invention
The present invention relates to a positive electrode for a lithium-ion secondary battery and a method for forming the positive electrode.
2. Description of the Related Art
In recent years, portable electronic devices such as mobile phones and laptop personal computers have rapidly become common, and the demand for smaller size and higher capacity of batteries which are drive power sources thereof has been increased. As a battery used for a portable electronic device, a lithium-ion secondary battery which has advantages of high energy density and high capacity has been widely used.
A lithium-ion secondary battery includes a positive electrode containing an active material such as lithium cobaltate, a negative electrode formed of a carbon material capable of occluding/releasing lithium, such as graphite, and an electrolyte solution in which an electrolyte containing a lithium salt such as LiBF4 or LiPF6 is dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate. Such a battery is charged and discharged by movement of lithium ions between a positive electrode and a negative electrode.
Further, a binder is used in order that active materials or an active material and a current collector are bound to each other. A binder is a polymer organic compound and has significantly poor conductivity. Therefore, when a large amount of a binder is used as compared with an active material, the proportion of the active material in the electrode is decreased; thus, capacity is decreased. In view of the above, a conductive additive such as acetylene black is mixed in order to improve conductivity (see Patent Document 1). In the case of using an active material with low conductivity, its conductivity is increased by microparticulation and carbon coating in some cases.